Pole upset by a girl (4)
I believe the answer is:
dora
'girl' is the definition.
(girl's name)
'pole upset by a' is the wordplay.
'pole' becomes 'rod' (synonyms).
'upset' shows that the letters should be reversed in order.
'by' is a charade indicator (letters next to each other).
'rod' backwards is 'dor'.
'dor'+'a'='DORA'
(Other definitions for dora that I've seen before include "David Copperfield's 'child-wife'" , "This girl" , "Bryan" .)